Why is the fertilization membrane important in sea urchin eggs?

The fertilization membrane is a critical structure that forms on the surface of a sea urchin egg immediately following fertilization. Its primary importance lies in its role in the prevention of polyspermy, which is the penetration of an egg by more than one spermatozoon.12

The formation process begins when a spermatozoon attaches to the egg, triggering the release of cortical granules into the space between the egg surface and the vitelline membrane. The contents of these granules merge with the vitelline membrane to thicken and harden it, creating the fertilization membrane. If this fusion process is prevented, the membrane remains thin and soft, failing to provide the necessary protection for the developing zygote. By establishing this barrier, the egg ensures that only one sperm nucleus successfully fuses with the egg nucleus, which is essential for normal development.12